This invention relates to a lightweight gas-metal composite with isolated particle-stabilized pores, particularly a lightweight aluminum composite, and its production.
Lightweight foamed metals have high strength-to-weight ratios and are extremely useful as load-bearing materials and as thermal insulators. Metallic foams are characterized by high impact energy absorption capacity, low thermal conductivity, good electrical conductivity and high absorptive acoustic properties.
Foamed metals have been described previously, e.g. in U.S. Pat. Nos. 2,895,819, 3,300,296 and 3,297,431. In general such foams are produced by adding a gas-evolving compound to a molten metal. The gas evolves to expand and foam the molten metal. After foaming, the resulting body is cooled to solidify the foamed mass thereby forming a foamed metal solid. The gas-forming compound can be metal hydride, such as titanium hydride, zirconium hydride, lithium hydride, etc. as described in U.S. Pat. No. 2,983,597.
A recent development in the production of lightweight foamed metal is described in Jin, U.S. Pat. No. 4,973,358, issued Nov. 27, 1990. In that patent, a composite of a metal matrix and finely divided solid stabilizer particles was heated above the liquidus temperature of the metal matrix and gas bubbles were discharged into the molten metal composite below the surface to thereby form a foamed melt on the surface of the molten metal composite. When this foam was cooled, it formed a solid foamed metal having a plurality of closed cells. The cells of this foam were large and had a polygonal structure with quite thin walls between the cells. Such foams in the liquid state are not amenable to shape casting and forming, since the applied forces tend to breakup the fragile cell structure. For example, it is difficult to conformably fill an open mold with this material. Even gentle urgings with a spatula or a similar tool tends to destroy the foam.
It is the object of the present invention to produce a lightweight gas-metal composite which is capable of being subjected to forming procedures without destroying its structural integrity.